Luciferases are enzymes that catalyze the oxidation of a substrate (e.g., luciferin or coelenterazine) with the concomitant release of photons of light. Luciferases have been isolated from numerous species, including Coleopteran arthropods and many sea creatures as well as bacteria. Because it is easily detectable and its activity can be quantified with high precision, luciferases have been widely used to study gene expression and protein localization. Unlike green fluorescent protein (GFP), which requires up to 30 minutes to form its chromophore, the products of luciferases can be detected immediately upon completion of synthesis of the polypeptide chain (if substrate and oxygen are also present). In addition, no post-translational modifications are required for enzymatic activity, and the enzyme contains no prosthetic groups, bound cofactors, or disulfide bonds. Luciferases are useful reporters in numerous species and in a wide variety of cells.
Luciferases possess additional features that render them particularly useful as reporter molecules for biosensing, i.e., molecules which reveal molecular properties of a system. Most catalytic reactions generate less than the energy of hydrolysis for two molecules of ATP, or about 70 kJ/mole. However, the luminescence elicited by luciferases has much higher energy content. For instance, the reaction catalyzed by firefly luciferase (560 nm) emits 214 kJ/mole of energy. Furthermore, luciferases are also highly efficient at converting chemical energy into photons, i.e., they have high quantum yields. Luciferases are thus extremely efficient for generating detectable signals.